With a rotating electrical machine there is a possibility of a locked state arising where rotation stops, due to equilibrium between the output and load of the machine. For example, in a controller for a rotating electrical machine for driving a vehicle, when there is a balance between retreating of a vehicle that is on an uphill path due to the vehicle weight, and forward motion due to motor torque, the rotating electrical machine may become locked or stalled. When the rotating electrical machine is of a multiphase drive type, if it enters a locked state, since the operating state of the multiphase coils is fixed, for example, if one of the multiphase coils is at maximum current in the locked state that maximum current state will continue. Therefore, depending on the situation, there is a possibility of a coil in which that maximum current flows, and switching elements connected to that coil, being damaged.
For example, in patent document 1 it is described that with a motor drive unit, if the boosting ratio of a boosting converter remains large when the motor is locked, switch elements of an inverter will be damaged because of current crowding, while on the other hand if the boosting ratio is uniformly lowered there is motor torque instability, and it is necessary to take these two scenarios into consideration. Here, the boosting ratio of the boosting converter is set to an operating point at which it is possible to keep torque equal and make motor drive voltage lower.
Also, in connection with the structure of the present invention, in patent document 2 it is disclosed that an electric vehicle comprises a power supply unit, high voltage auxiliary equipment as a load to which electrical power is supplied from the power supply unit, and an electric motor connected to the power supply unit via a drive inverter, having wiring provided between the power supply unit and the load, wherein power is exchanged between the power supply unit and the load via this wiring. Here, it is described that the power supply unit has a fuel cell, capacitor, a secondary battery and a DC/DC converter respectively connected to the wiring, and a switch for switching connection states of the fuel cell is provided in the wiring.
Patent document 1: JP 2007-124746
Patent document 2: JP 2003-187816
In patent document 1 boosting control when a rotating electrical machine enters a locked state is described, and in patent document 2 a power supply unit including a fuel cell is described. The documents describe respectively separate related art technology, but there is no description of control of a power supply unit that includes a fuel cell, in a system including a fuel cell and a rotating electrical machine, capable of preventing damage to switching elements when the rotating electrical machine enters a locked state.
An object of the present invention is to provide a power supply controller, in a system including a fuel cell and an electrical rotating machine, capable of preventing damage to switching elements when the rotating electrical machine enters a locked state.